Multigigahertz bandwidth FM response of frequency tunable two-electrode DFB lasers

The FM response of frequency-tunable two-electrode distributed-feedback (DFB) lasers operating at 1.35 mu m is discussed. Under certain bias conditions, an FM response of approximately 1 GHz/mA is flat over a range of modulating frequencies from 10 kHz to several hundred megahertz. This region is followed by a shallow dip and a high-frequency relaxation resonance peak, allowing an overall 3-dB FM bandwidth of approximately 5 GHz. This is believed to be the widest FM bandwidth reported to date for such lasers; however, variations of the phase of the FM response could limit the useful bandwidth in a frequency-shift keying (FSK) system. The experimental response is a function of static tuning conditions, with significant differences between regions of red and blue frequency shift with increasing current. The observed behavior is well represented by theoretical curves derived from a small-signal analysis.<>